1. Field of the Invention
The present invention generally relates to a semiconductor device. More specifically, the present invention relates to a semiconductor device including a transistor having a low threshold voltage and a high breakdown voltage.
2. Description of the Related Art
Various electronic devices such as computers, telecommunication devices, electric home appliances and so forth include integrated circuits formed of electronic components such as transistors, resistors, capacitors and inductors in order to perform specific functions. With an increasing demand for multiple and high functionality in the field of electronic devices, there is a tendency that electronic components used in integrated circuits become multi-functional and more complex.
However, kinds of electronic components used in semiconductor devices are limited due to an overall process characteristic of semiconductor fabricating processes. In other words, unlike a mode for individually assembling parts formed as occasion demands, e.g., in the production of an automobile, electronic components used in a semiconductor device are fabricated collectively through a series of processes. As a result, in order to form various kinds of electronic components, there is a need to increase the number of fabricating process steps. However, because of a disadvantage associated with increasing fabrication costs and a defect rate, it is necessary to limit a kind of electronic component used in semiconductor devices.
Transistors determinately influence characteristics such as size, speed, usable time, and power dissipation. For example, ordinary advanced semiconductor devices, e.g., a LCR driver IC (LDI), include a high-voltage transistor having a high breakdown voltage characteristic and a low-voltage transistor having a low threshold voltage characteristic.
However, the high-voltage transistor is weak as compared with the low-voltage transistor with regard to performance of transistors. The reason for this weakness is that the resistance between a source/drain of the high-voltage transistor is high in a turn-on state. In addition, due to a wide dispersion of a threshold voltage by a thick gate insulating layer, the high-voltage transistor has technical difficulties in the areas of a matching property or a mixed signal property. The low-voltage transistor has an excellent performance characteristic, as well as a narrow dispersion of a threshold voltage, but has a low breakdown voltage. As a result, the low-voltage transistor is not used in the field of circuits where a high voltage is applied. For electronic devices requiring excellent and varied functions, a new transistor, which has a narrow dispersion of a threshold voltage and is suitable for use in the field of circuits where a high voltage is applied, is required. However, the structure of such a new transistor should have a processing compatibility with low-voltage and high-voltage transistors to avoid increasing fabrication costs and a defect rate.